1. Field of the Invention
The present invention relates to a fuel injection valve, in which injection amount and injection timing are controlled by changing fuel pressure of a pressure control chamber.
2. Description of the Prior Art
A common rail fuel injection system, in which high pressure fuel accumulated in a common rail is injected into a combustion chamber, is well known. A fuel injection valve (injector), which is applicable to the common rail fuel injection system, has a pressure control chamber, whose pressure is controlled by fuel supplied thereto through an entrance orifice provided in a fuel flow-in passage and ejected therefrom through an exit orifice provided in a fuel flow-out passage for giving backpressure to a control piston movable together with a needle. The injection amount and injection timing are variable based on a change of the fuel pressure of the pressure control chamber (backpressure to the control piston).
The fuel pressure of the pressure control chamber is changed by an electromagnetic valve that is operative to open and close the fuel flow-out passage including the exit orifice through which the pressure control chamber communicates with a low pressure source.
In the injector mentioned above, it is required to accurately control not to fluctuate the fuel pressure of the pressure control chamber for securing a stable injection. To this end, it is important to accurately regulate and stabilize flow amount of fuel passing, in particular, through the entrance orifice provided in the fuel flow-in passage to the pressure control chamber.
To accurately regulate and stabilize the flow amount of fuel through the entrance orifice, length, diameter and position of the entrance orifice are main factors on designing the same. On designing the position thereof, it is inevitable that an outlet of the entrance orifice has to be exposed to a relatively large space for adequately attenuating fuel flow energy. For example, in the injector disclosed in U.S. Pat. No. 6,027,037, the outlet of the entrance orifice is connected to the pressure control chamber via a groove whose volume is relatively large so that the flow amount of fuel through the entrance orifice is stable. However, in the conventional injector disclosed in U.S. Pat. No. 6,027,037, a first plate in which the entrance orifice is formed and a second plate in which the exit orifice is formed are different members. This causes an inconvenience, on adjusting length of the entrance orifice for securing a target flow amount of fuel, that a change of enlarging the length of the entrance orifice is not sufficiently free, since the entrance orifice is limited to be positioned within the first plate whose thickness is relatively thin. Therefore, in this case, instead of enlarging the length of the entrance orifice, the diameter of the entrance orifice is obliged to be reduced for the adjustment of fuel flow. However, a slight change of the diameter of the entrance orifice is likely to affect largely on the fuel flow amount, compared with a slight change of the length of the entrance orifice. Accordingly, the change of the diameter of the entrance orifice is not preferable for a purpose of the fuel flow adjustment.
An object of the present invention is to provide a fuel injection valve having a piece of plate in which both of an entrance orifice and an exit orifice are formed so that length of the entrance orifice is easily changed for adjusting a flow amount of fuel passing therethrough to a target value.
To achieve the above objects, in the fuel injection valve having a pressure control chamber to which fuel is supplied from high pressure source via a fuel flow-in passage including an entrance orifice and from which the fuel is ejected to a low pressure source via a fuel flow-out passage including an exit orifice, a nozzle provided with a needle making an axial and reciprocal movement in response to fuel pressure in the pressure control chamber and with an injection hole to be opened and closed by the movement of the needle, and an electromagnetic valve operative to allow and interrupt a fuel communication between the fuel flow-out passage and the low pressure source for controlling the fuel pressure in the pressure control chamber, the fuel flow-in passage, the fuel flow-out passage and at least a part of the pressure control chamber are formed in a single piece of a plate. The part of the pressure control chamber is opened to an axial end surface of the plate and the fuel flow-out passage extends so as to penetrate the plate axially from an inner wall of the part of the pressure control chamber to another axial end surface of the plate. The fuel flow-in passage comprises a first passage extending from the axial end surface of the plate and a second passage extending from the inner wall of the part of the pressure control chamber, which intersect with each other within the plate. The entrance orifice is formed in one of the first and second passages.
It is preferable that one of the first and second passages is a blind passage and at least a part of the other of the first and second passages is the entrance orifice running into the blind passage. In case that the first passage is the blind passage, an end of the entrance orifice of the second passage is opened to the inner wall of the part of the pressure control chamber and another end thereof is opened to a vicinity of a dead end of the blind passage.
On the other hand, in case that the second passage is the blind passage whose inner diameter is axially substantially uniform, the first passage is provided at an end thereof on a side of the second passage with the entrance orifice opened to the blind passage at a position away by more than 0.2 mm from a dead end thereof. Preferably, the entrance orifice of the first passage is connected substantially perpendicularly to the second passage.
Further, it is preferable that an angle of the first passage to the axial end surface of the plate, which is an angle opposed to the second passage, falls within a range from 25xc2x0 to 90xc2x0 and an angle of the second passage to the axial end surface of the plate, which is an angle opposed to the first passage, falls within a range from 15xc2x0 to 55xc2x0.
Furthermore, it is preferable that the inner wall of the part of the pressure control chamber is at least partly a conical shape inner wall whose diameter is larger toward the axial end surface of the plate and to which the second passage is opened.
Moreover, it is preferable that an extended axial line of the second passage passes through inside of the part of the pressure control chamber without running against the inner wall thereof.